Reciprocal Full‐Sib Recurrent Selection in Maize: II. Contributions of Additive, Dominance, and Genetic Drift Effects

Abstract

Reciprocal full‐sib recurrent selection emphasizes selection for additive and nonadditive genetic effects, and direct response is measured in the population crosses. Our objectives were to determine the contributions of additive and dominance effects to the response of selection and to estimate effects of genetic drift after eight cycles of reciprocal full‐sib recurrent selection (for grain yield) in maize (Zea mays L.) populations BS10 and BS11. The BS10 and BS11 populations and their crosses corresponding to Cycles 0, 2, 4, 6, and 8 were evaluated at two levels of inbreeding (F = 0 and F = 0.5) across eight environments for grain yield and moisture, stalk and root lodging, ear height, prolificacy, and days to anthesis. Population means were compared to estimate the contributions of genetic effects. The contributions of heterozygotes to the means of BS10CO and BS11CO were more important than homozygotes for grain yield, whereas the contributions of homozygotes were more important for grain moisture, prolificacy, standability, days to anthesis, and ear height. Significant heterosis was detected between BS10CO and BS11CO for grain yield. Heterosis for grain yield of the interpopulation crosses increased with selection and was caused by the accumulation of favorable alleles with additive and dominant effects from both populations and the heterozygous condition at loci for which genetic drift had caused fixation of alleles in one of the parental populations. Effects of genetic drift were significant for grain yield (BS10 and BS11), days to anthesis (BS10), and ear height (BS11). The improved grain yield of the parent populations over cycles of selection was attributed mainly to alleles with additive (BS11) and dominant effects (BS10). Means of selected BS10 and BS11 populations, adjusted for genetic drift, indicate that the difference between direct and indirect rates of response to selection for gram yield was not significant. The effects of assortative mating during progeny formation and small effective population sizes during recombination of selected progenies should be considered in longterm reciprocal full‐sib recurrent selection programs, particularly if improved performance of the parent populations is desired.

Identification of heterotic patterns between expired proprietary, NDSU, and industry short-season maize inbred lines

“…Heterotic groups represent groups of germplasm sources that when crossed with each other produce consistently better crosses than when crosses are made within those groups (Hallauer and Carena 2009). Identifying heterotic patterns, which are crosses between known genotypes (from different heterotic groups) expressing a high level of heterosis (Carena and Hallauer 2001, Troyer 2006, Mendes et al 2015, is key to the development of successful maize hybrids (Eyherabide and Hallauer 1991, Barata and Carena 2006, Carena and Wicks III 2006. The North American dent maize germplasm is composed of multiple heterotic groups that when crossed to each other can optimize hybrid performance (Mikel and Dubley 2006).…”

Deriva genética de caracteres quantitativos em milho

“…Moreira (1999), avaliando as mesmas subpopulações não autofecundadas em apenas dois ciclos de deriva genética, encontrou valores de DEN em relação à população original de 6,74% e 5,62% para C1 e C2 da população BR-105 e de 7,86% (C1) e 9,87% (C2) para a população BR-106. Blandón (1996) (SMITH, 1979b;SMITH 1983, HELMS;SMITH, 1989;EYHERABIDE;HALLAUER, 1991;CEPEDA et al, 2000;BUTRUILLE et al, 2004;FLACHENECKER et al, 2006 Considerando o caráter NFE, observa-se que para as duas populações as médias não foram significativas em nenhum ciclo e a quantidade de estimativas significativas em todos os ciclos foi aproximada. Na população BR-105, das dezessete estimativas significativas, oito foram positivas e nove negativas e, na população BR-106, todas as estimativas foram negativas.…”

“…Foram observados efeitos significativos para a deriva genética (DQI) que afetaram o desempenho per se das populações, atuando em sentido contrário ao do progresso com a seleção. A magnitude desses efeitos foi bastante variável, demonstrando a importância da deriva genética como fator limitante ao progresso obtido com a seleção na cultura do milho (SMITH, 1984;TRAGESSER et al, 1989;HELMS;SMITH, 1989;EYHERABIDE;HALLAUER, 1991;LANDI;FRASCAROLI, 1993;STOJŠIN;KANNENBER, 1994;REZENDE, 1997;CEPEDA et al, 2000;BUTRUILLE et al, 2004;FLACHENECKER et al, 2006).…”

“…As primeiras estimativas obtidas foram em populações de milho submetidas à seleção recorrente, em que foram observados efeitos significativos e de magnitude variável, afetando o desempenho per se das populações e impondo limitações ao progresso com seleção (TRAGESSER et al, 1989;HELMS;SMITH, 1989;EYHERABIDE;HALLAUER, 1991;LANDI;FRASCAROLI, 1993;STOJŠIN;KANNENBER, 1994;REZENDE, 1997;CEPEDA et al, 2000;BUTRUILLE et al, 2004;FLACHENECKER et al, 2006). Todavia, essas estimativas se encontram confundidas com os efeitos da seleção, não refletindo os reais efeitos da deriva genética.…”

“…Keywords: Effective population size; Inbreeding depression; Morphological traits; Population structure; Zea mays L. (TRAGESSER et al, 1989;EYHERABIDE;HALLAUER, 1991;LANDI;FRASCAROLI, 1993;REZENDE, 1997;CEPEDA et al, 2000;BUTRUILLE et al, 2004;FLACHENECKER et al, 2006). Entretanto, essas estimativas estão confundidas com os efeitos da seleção e, possivelmente, não refletem os reais efeitos da deriva genética.…”